1. Field of the Invention
Embodiments of the present invention generally relate to a gasification system, and more particularly to an injector and a method for co-feeding solid and liquid fuels into a gasifier of the gasification system.
2. Description of the Prior Art
Gasifiers are generally used to convert a mixture of fuel and an oxidizing stream into hydrogen and CO, generally referred to as “syngas.” The syngas has many industrial applications. For example, the syngas is used to produce electricity in an IGCC (Integrated Gasification Combine Cycle) plant, or to produce chemicals in a chemical plant. Gasifiers are generally divided into two types, depending upon the form of the feedstock (fuel): dry feed gasifiers and liquid feed gasifiers. Both of the dry feed gasifiers and the liquid feed gasifiers have advantages and disadvantages. In recent years, however, the dry feed gasifiers development has had attraction for their wide fuel flexibility and higher efficiency.
In gasification systems, injectors are employed to inject feedstock into gasifiers. A conventional injector for feeding a gasifier generally has two channels: a first channel and a second channel. The first channel is used to pneumatically convey a solid fuel such as a pulverized coal or a liquid fuel such as a coal slurry, and the second channel is used to convey an oxidizing stream for dispersing the solid fuel or the liquid fuel into the gasifier.
During gasification process, fly ash (fine particles) containing unconverted coal is generated along with the syngas. The fine particles in the syngas will be captured in a syngas water-scrubbing unit. For utilizing the unconverted carbon contained in the fine particles, it is desired to recycle the fine particles back to the gasifier. However, the fine particles are generally mixed with wastewater from the syngas water-scrubbing unit to form a stream (referred to as “recycled fines slurry” thereafter) that is difficult to be directly mixed with solid fuel such as pulverized coal.
Therefore, if using the conventional injector for feeding the solid fuel, mixing between the recycled fines slurry and the solid fuel is difficult. Furthermore, it leads to reduced flowability of the solid fuel and decreased uniformity of fuel concentration in the gasifier, resulting in less efficient gasification performance. There is a need for an improved injector for co-feeding recycled fines slurry and solid fuel to improve gasification performance.